1. Field of the Invention
The invention relates generally to serial attached SCSI (“SAS”) domains and more specifically to testing of responses to stimuli applied to SAS device controllers or SAS expanders.
2. Discussion of Related Art
Small Computer Systems Interface (“SCSI”) is a set of American National Standards Institute (“ANSI”) standard electronic interface specification that allow, for example, computers to communicate with peripheral hardware. Common SCSI compatible peripheral devices may include: disk drives, tape drives, Compact Disc-Read Only Memory (“CD-ROM”) drives, printers and scanners. SCSI as originally created included both a command/response data structure specification and an interface and protocol standard for a parallel bus structure for attachment of devices. SCSI has evolved from exclusively parallel interfaces to include both parallel and serial interfaces. “SCSI” is now generally understood as referring either to the communication transport media (parallel bus structures and various serial transports) or to a plurality of primary commands common to most devices and command sets to meet the needs of specific device types as well as a variety of interface standards and protocols.
The collection of primary commands and other command sets may be used with SCSI parallel interfaces as well as with serial interfaces. The serial interface transport media standards that support SCSI command processing include: Fibre Channel, Serial Bus Protocol (used with the Institute of Electrical and Electronics Engineers 1394 FireWire physical protocol; “IEEE 1394”) and the Serial Storage Protocol (SSP).
SCSI interface transports and commands are also used to interconnect networks of storage devices with processing devices. For example, serial SCSI transport media and protocols such as Serial Attached SCSI (“SAS”) and Serial Advanced Technology Attachment (“SATA”) may be used in such networks. These applications are often referred to as storage networks. Those skilled in the art are familiar with SAS and SATA standards as well as other SCSI related specifications and standards. Information about such interfaces and commands is generally obtainable at the website http://www.t10.org.
Such SCSI storage networks are often used in large storage systems having a plurality of disk drives to store data for organizations and/or businesses. The network architecture allows storage devices to be physically dispersed in an enterprise while continuing to directly support SCSI commands directly. This architecture allows for distribution of the storage components in an enterprise without the need for added overhead in converting storage requests from SCSI commands into other network commands and then back into lower level SCSI storage related commands.
A SAS network typically comprises one or more SAS initiators coupled to one or more SAS targets often via one or more SAS expanders. In general, as is common in all SCSI communications, SAS initiators initiate communications with SAS targets. The expanders expand the number of ports of a SAS network domain used to interconnect SAS initiators and SAS targets (collectively referred to as SAS devices or SAS device controllers).
It is a particular problem to thoroughly test SAS device controllers and SAS expanders as regards the full complement of possible responses to command, status or data exchanges and associated anomalous conditions. For example, it is a particular difficulty to verify proper operation of a SAS device controller or SAS expander in response to certain anomalous communication conditions such as BREAK, BROADCAST, and NAK conditions, or CRC errors, or invalid protocols or packets, etc.
Prior techniques address this testing dilemma through external SAS emulators to generate a variety of stimuli including anomalous conditions and SAS analyzers to detect and verify the response from the SAS device controller or SAS expander under test. An exemplary SAS emulator may be programmed by a user to generate particular desired sequences and apply the desired sequences as a stimulus to the attached SAS expander or SAS device controller. The response generated may then be captured and analyzed to verify proper operation. Though the emulation and analyzer features may be integrated in a single test component, such external SAS analyzers and emulators can be costly devices. Furthermore, coupling an external test component to the SAS device controller or SAS expander under test may induce undesirable characteristics into the system under test. Since the external SAS analyzer or emulator must couple into the transport media coupled to the SAS device controller or SAS expander under test, by definition the analysis and testing is not performed in a real world environment in which the system may be normally configured.
It is evident from the above discussion that a need exists for improved testing of SAS device controllers and SAS expanders in an environment more closely resembling real world application environments in which the SAS device controller or SAS expander may be configured.